1. Field of the Invention
The present invention relates generally to color image reproducing apparatus and, more particularly, is directed to a color image reproducing apparatus which is adapted to be used as a color view finder for a color image pick-up apparatus.
2. Description of the Prior Art
It has been proposed to utilize a color image reproducing apparatus of the shadow mask type as a color view finder for a color image pick-up apparatus. With this type of color image reproducing apparatus, a shadow mask type color cathode ray tube which utilizes three electron beams in provided, each beam being density modulated by the red, green and blue primary color signals, respectively, as the electron beams scan respective color phosphor elements arranged on the color phosphor screen of the cathode ray tube. However, in order for the density modulated electron beams to correctly impinge on corresponding color phosphor elements so as to prevent color misregistration or misalignment, complicated circuitry must generally be provided. For example, a convergence circuit and the like are generally provided, resulting in the circuitry having a complicated construction and being difficult to adjust.
It has also been proposed to use a color image reproducing apparatus of the beam index type in which the display screen of the cathode ray tube has periodic index stripes, in addition to the usual beam-excitable red, green and blue color phosphor stripes. The color phosphor stripes are arrayed in red, green and blue triads, repetitively across the display screen so as to be scanned by the electron beam as the latter effects a horizontal line scan in, for example, left-to-right traverse. As the electron beam scans the color phosphor stripes, it also scans the index stripes, which typically are also phosphor stripes that emit light when excited by the scanning electron beam. A photo-detector responds to each excited phosphor index stripe to produce a periodic signal, the frequency of which is equal to the frequency at which the phosphor index stripes are excited. Thus, as the electron beam scans a horizontal line across the display screen, the photo-detector generates a periodic index signal which is used to gate red, green and blue color control signals onto, for example, the first grid of the cathode ray tube in a successive sequence. Thus, the gating of the respective color control signals is desirably synchronized with the beam velocity. This means that when the beam moves into scanning alignment with, for example, a red phosphor stripe, the red control signal is gated so as to density modulate the beam with the red signal information. Then, as the beam moves into proper scanning alignment with a green phosphor stripe, the red control signal is interrupted and the green control signal is gated so as to modulate the beam. Similarly, when the beam next moves into proper scanning alignment with a blue phosphor stripe, the green control signal is interrupted and the blue control signal is gated to density modulate the beam. The foregoing gating sequence is repeated so that, as the beam scans the red, green and blue phosphor elements, it is concurrently and synchronously modulated with red, green and blue color information.
However, due to scattering of the electron beam during the scanning between adjacent index phosphor stripes and because of the time delay of the detected signals and the like, it is extremely difficult to control the electron beam to correctly impinge upon the color phosphor stripe corresponding to the density modulation of the electron beam by the respective primary color signal. Accordingly, in such case, additional circuitry is necessary to cause the electron beam to correctly impinge upon the color phosphor stripes, and the circuit construction becomes relatively complicated.
Further, with the above shadow mask type and beam index type color image reproducing apparatus, any reduction in the size of the color phosphor phosphor elements or stripes arranged on the phosphor screen is limited. In other words, when the color image reproducing apparatus of the shadow mask type or the beam index type is reduced in size, the picture elements, that is, the color phosphor elements and stripes, cannot be accurately constructed and therefore become dimensionally rough, resulting in a deterioration in the resolution of the picture. However, it is desirable that a color image reproducing apparatus, which is used as a color view finder for a color image pick-up apparatus, be of a relatively small size.